Filtration method using polyimide nanoweb with amidized surface and apparatus therefor

Abstract

The present invention is directed to the preparation and use of aromatic polyimide nanowebs with amide-modified surfaces. Uses include as a filtration medium, and as a separator in batteries, particularly lithium-ion batteries. The invention is also directed to a method comprising the aromatic polyimide nanoweb with amide-modified surface. The invention is further directed to a multi-layer article comprising the aromatic polyimide nanoweb with amide-modified surface, and to an electrochemical cell comprising the multi-layer article.

We claim: 
     
       1. A method for filtering comprising causing a mixture of a solid and a fluid to wettably impinge upon the surface of a surface modified polyimide nanoweb in such manner that a fluid-rich portion of said mixture is transported through said surface-modified polyimide nanoweb, while a solid-rich portion of said mixture is not so transported; and, wherein said surface-modified polyimide nanoweb comprises a nanoweb consisting essentially of nanofibers of fully aromatic polyimide, said nanoweb having a free surface area at least a portion of which is chemically modified by reaction with a primary amine to form a secondary amide comprising a functional group comprising a hydrocarbon radical. 
     
     
       2. The method of  claim 1  wherein said functional group further comprises a functional group comprising oxygen, sulfur or nitrogen. 
     
     
       3. The method of  claim 2  wherein said functional group is an amine. 
     
     
       4. The method of  claim 1  wherein said nanofibers are characterized by a number average diameter in the range of 50 to 500 nanometers. 
     
     
       5. The method of  claim 4  wherein said nanofibers are characterized by a number average diameter in the range of 100 to 400 nanometers. 
     
     
       6. The method of  claim 1  wherein said hydrocarbon radical is a saturated hydrocarbon radical. 
     
     
       7. The method of  claim 6  wherein said saturated hydrocarbon radical is an alkyl radical. 
     
     
       8. The method of  claim 7  wherein said alkyl radical is a n-alkyl radical. 
     
     
       9. The method of  claim 8  wherein said n-alkyl radical has 15 to 20 carbon atoms. 
     
     
       10. The method of  claim 1  wherein said fully aromatic polyimide is PMDA/ODA. 
     
     
       11. An apparatus comprising a housing provided with a first port for introducing a mixture to be filtered, and a second port for discharging a filtrate, said housing comprising a surface-modified aromatic polyimide nanoweb therewithin sealingly disposed to be wettably impinged upon the surface thereof by said mixture to be filtered in such manner that a fluid-rich portion of said mixture is transported through said surface-modified polyimide nanoweb, while a solid-rich portion of said mixture is not so transported; and, wherein said surface-modified polyimide nanoweb comprises a nanoweb consisting essentially of nanofibers of fully aromatic polyimide, said nanoweb having a free surface area at least a portion of which is chemically modified by reaction with a primary amine to form a secondary amide comprising a functional group comprising a hydrocarbon radical. 
     
     
       12. The apparatus of  claim 11  wherein said functional group further comprises a functional group comprising oxygen, sulfur or nitrogen. 
     
     
       13. The article of  claim 12  wherein said functional group is an amine. 
     
     
       14. The apparatus of  claim 11  wherein said nanofibers are characterized by a number average diameter in the range of 50 to 500 nanometers. 
     
     
       15. The apparatus of  claim 14  wherein said nanofibers are characterized by a number average diameter in the range of 100 to 400 nanometers. 
     
     
       16. The apparatus of  claim 11  wherein said hydrocarbon radical is a saturated hydrocarbon radical. 
     
     
       17. The apparatus of  claim 16  wherein said saturated hydrocarbon radical is an alkyl radical. 
     
     
       18. The apparatus of  claim 17  wherein said alkyl radical is a n-alkyl radical. 
     
     
       19. The apparatus of  claim 18  wherein said n-alkyl radical has 15 to 20 carbon atoms. 
     
     
       20. The apparatus of  claim 11  wherein said fully aromatic polyimide is PMDA/ODA.